Virtual local area networks (VLANs) represent a domain in which a client can send frames to any other client in the same VLAN. Private VLANs allow sharing on a single (primary VLAN) by clients on secondary VLANs. Clients on secondary VLANs can communicate with one another unless configured as an isolated VLAN. With conventional networks, if two switches terminate private VLANs, traffic that should be isolated can still make it across to the hosts behind the other switch, if both switches are configured to use the same primary VLAN. This may be prevented by configuring different primary VLANs, however, there are a number of drawbacks to this approach. For example, IP addressing changes may be required.
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